1. Technical Field
The present technology relates to a method for manufacturing a bladder for use in manufacturing tires, and more particularly relates to a method for manufacturing a bladder for use in manufacturing tires configured so as to have superior release performance between a tire and a bladder when the tire is manufactured, and enhanced sustainability thereof.
2. Related Art
Generally, vulcanization molding of pneumatic tires is performed by vulcanizing while pressing an outer surface of an unvulcanized tire against an inner surface of a vulcanizing mold. The unvulcanized tire is placed in the vulcanizing mold, a heating/pressurizing medium such as steam or the like is pressure injected into a rubber pouch-shaped bladder inserted into a cavity of the unvulcanized tire, and the unvulcanized tire is expanded. The bladder is generally formed from a butyl rubber, and therefore there is vulcanization adhesion between the bladder and an inner liner made from halogenated butyl rubber, or the like, disposed on an inner circumferential surface of the unvulcanized tire. Therefore, releaseability is inferior when the bladder is shrunk and removed from the pneumatic tire after vulcanization. There are thus problems with damage and the like to the inner liner of the tire inner circumferential surface.
To solve these problems, measures have been implemented such as applying release agents made from various types of silicone and the like to an outer surface of the bladder or the inner circumferential surface of the unvulcanized tire, or forming a layer of a release agent by applying a release agent to the outer surface of the bladder and then curing said release agent. However, the release agent must be applied at each vulcanization molding because a release effect of the release agent is not sustained for a long period of time by simply applying the release agent. Therefore, the effects on workability and the working environment are problems. Additionally, when forming a layer of a release agent by applying a release agent made from various types of silicone, or the like, to the outer surface of the bladder and curing, while there is a slight increase in release performance, the layer of the release agent cracks and peels as a result of repeated expansion and contraction of the bladder at vulcanization molding. Therefore, it has not been possible to sufficiently sustain release performance.
For this reason, Japanese Patent No. 3316034 proposes forming a lubrication layer with release properties made from two layers, a silicone rubber layer and a silicone resin layer, on the outer surface of the bladder. However, with this method, because the outer surface of the resin cross-linked bladder is surface-treated, the reactivity of the silicone rubber with butyl rubber molecules is low, and the silicone rubber layer peels due to repeated expansion and contraction of the bladder at vulcanization molding. Therefore, insufficient sustainability of the release effect has been a problem.